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[PATCH] namei fixes (9/19)

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New helper: __follow_mount(struct path *path).  Same as follow_mount(), except
that we do *not* do mntput() after the first lookup_mnt().

IOW, original path->mnt stays pinned down.  We also take care to do dput()
before mntput() in the loop body (follow_mount() also needs that reordering,
but that will be done later in the series).

The following are equivalent, assuming that path.mnt == x:
(1)
	follow_mount(&path.mnt, &path.dentry)
(2)
	__follow_mount(&path);
	if (path->mnt != x)
		mntput(x);
(3)
	if (__follow_mount(&path))
		mntput(x);

Callers of follow_mount() in __link_path_walk() converted to (2).

Equivalent transformation + fix for too-late-mntput() race in __follow_mount()
loop.

Signed-off-by: Al Viro <viro@parcelfarce.linux.theplanet.co.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Al Viro 2005-06-06 13:36:05 -07:00 committed by Linus Torvalds
parent d671d5e514
commit 463ffb2e9d
1 changed files with 23 additions and 2 deletions
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25
fs/namei.c
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@ -576,6 +576,23 @@ int follow_up(struct vfsmount **mnt, struct dentry **dentry)
/* no need for dcache_lock, as serialization is taken care in
* namespace.c
*/
static int __follow_mount(struct path *path)
{
int res = 0;
while (d_mountpoint(path->dentry)) {
struct vfsmount *mounted = lookup_mnt(path->mnt, path->dentry);
if (!mounted)
break;
dput(path->dentry);
if (res)
mntput(path->mnt);
path->mnt = mounted;
path->dentry = dget(mounted->mnt_root);
res = 1;
}
return res;
}
static int follow_mount(struct vfsmount **mnt, struct dentry **dentry)
{
int res = 0;
@ -778,7 +795,9 @@ static fastcall int __link_path_walk(const char * name, struct nameidata *nd)
if (err)
break;
/* Check mountpoints.. */
follow_mount(&next.mnt, &next.dentry);
__follow_mount(&next);
if (nd->mnt != next.mnt)
mntput(nd->mnt);
err = -ENOENT;
inode = next.dentry->d_inode;
@ -836,7 +855,9 @@ static fastcall int __link_path_walk(const char * name, struct nameidata *nd)
err = do_lookup(nd, &this, &next);
if (err)
break;
follow_mount(&next.mnt, &next.dentry);
__follow_mount(&next);
if (nd->mnt != next.mnt)
mntput(nd->mnt);
inode = next.dentry->d_inode;
if ((lookup_flags & LOOKUP_FOLLOW)
&& inode && inode->i_op && inode->i_op->follow_link) {